Typically, as shown in FIG. 9, a dialyzer 1 has a cylindrical container containing a large number of hollow fiber semipermeable membrane capillaries, and allows exchange of blood in a patient body by passing the blood extracted from the patient body through the capillaries and supplying a dialysate, such as a physiologic saline, to the exterior of the capillaries to extract body fluids from the blood into the dialysate by the action of osmotic pressure across a semipermeable membrane and supply necessary substances to the blood. In order to pass the dialysate through the dialyzer 1, a dialysate tube 3 is connected via a socket 4 to a plug 2 provided at each of connection ports of inlet and outlet for the dialysate.
As shown in FIG. 10, the conventional socket 4 comprises a socket main body 5 having a coupling part 5a of the socket main body 5 to be connected to the plug 2 and a tube connecting cylindrical part 5b to be connected to the tube 3 for dialysate (see FIG. 9), a locking ball 6 for retaining the socket 4 and the plug 2 locked, a sleeve 7 fitted onto the coupling part 5a of the socket main body 5 to press the locking ball 6 in a locking direction, a coil spring 7a for biasing the sleeve 7, and an O-ring 8 provided on an inner surface of the coupling part 5a. 
In order to connect the socket 4 to the plug 2 on the dialyzer 1, after the sleeve 7 is retracted in a direction indicated by an arrow in this drawing to release the locking ball 6, the coupling part 5a of the socket 4 is fitted onto the plug 2, and then at a fitting reference position, the locking ball 6a is fitted into an annular groove 2a formed in the plug 2. If the sleeve 7 is released at this time, the sleeve 7, which is biased by the spring, biases the locking ball 6 in the locking direction, so that the socket 4 can be firmly attached to the plug 2.
By the way, in a dialysis treatment, while the dialyzer 1 and the plug 2 are disposed after the treatment, the socket 4 for connecting the plug 2 and the dialysate tube 3 (see FIG. 9) can be repeatedly used after cleaning and sterilization.
For example, there is an implemented method of dipping the socket 4 into a cleaning solution, or as shown in FIG. 11 a method of cleaning or disinfecting an inner wall of the socket 4 by connecting the socket 4 to a cleaning adapter 9 and circulating a cleaning solution or antiseptic solution therethrough.
In addition, a pore size of the dialysis membrane in the dialyzer has been increased in recent years, so that a possibility is pointed out that various germs or toxins produced by the germs are introduced from the dialysate into the blood. In particular, in the case of a dialysis filtration system based on a scheme of injecting blood into the dialyzer, if there is any germ or toxin in the dialysate, a problem arises that a patient is adversely affected, for example, becomes feverish, so that when the socket 4 is to be repeatedly used, it is actually desired that the socket 4 has a high cleanability.
As described above, when the conventional socket 4 for a dialyzer is attached to or removed from the plug 2 of the dialyzer 1, the sleeve 7 is retracted to release the locking ball 6 in the first step, and then the coupling part 5a is fitted onto the plug 2 and connected thereto at a normal position. Then, the sleeve 7 is released and spring-biases the locking ball 6 in the locking direction to complete the connection between the socket 4 and the plug 2. Thus, a problem has been pointed out that when the socket 4 is attached to or removed from the plug, two operations are needed respectively, which degrades the operability when connecting the socket 4.
Furthermore, since fitting of the socket 4 at the normal position is conducted intuitively, it takes a time to surely establish the connection, which is also a factor of degrading the operability when connecting the socket 4.
Besides, from the view point of repeatedly using the conventional socket 4 for a dialyzer, the inner wall of the coupling part 5a of the socket main body 5 of the conventional socket 4 can be cleaned to some degree, but an area overlapping with the cleaning adapter 9 cannot be cleaned, and furthermore, the O-ring 8, an O-ring accommodation groove 8a of the O-ring 8, a rear surface of the locking ball 6, the internal coil spring 7a and the like cannot be surely cleaned, so that the various germs may remain inside, which is an great obstacle to the repeated usings of the socket.
The present invention is devised in view of such a circumstance and aims to provide a socket for a dialyzer that can be attached to or removed from the plug of the dialyzer easily and surely with a single operation and in which not only the inner wall of the coupling part but also the rear side of the locking ball and the internal mechanism including the spring can be surely cleaned, so that it has hygienically no problem if used repeatedly, and a method for cleaning the socket.